1. Field of the invention
The present invention relates to a radiation image detector for recording a radiation image by irradiating an image-carrying radiation on the detector to store charges in proportion to the dose of the radiation irradiated on the detector and detecting the radiation image stored in the detector as electrical signals by scanning a linear reading light over the detector and reading out the charges stored in the detector at a predetermined readout timing.
2. Description of the Related Art
Radiation image detectors for recording a radiation image by storing charges in the storage section of the detector in proportion to the dose of radiation, such as X-ray transmitted through a subject are widely used for obtaining, for example, medical radiation images, and various types of the detectors have been proposed.
One such detector is proposed as described, for example, in Japanese Unexamined Patent Publication No. 2000-284056. The radiation image detector described above includes a radiation image recording medium having a set of layers layered in the order of a first electrode layer configured to transmit radiation; a recording photoconductive layer configured to generate charges when exposed to radiation; a charge transport layer configured to act as substantially an insulator against the charges of the latent image and as substantially a conductor for the transport charges having opposite polarity to that of the charges of the latent image; a reading photoconductive layer configured to generate charges when exposed to reading light; and a second electrode layer having first linear electrodes extending linearly and configured to transmit reading light, and second linear electrodes extending linearly and configured to block reading light, in which the first and second linear electrodes are disposed alternately in parallel. In the radiation image detector described above, the radiation is irradiated on the detector from the side of the first electrode layer, and the radiation image is recorded by storing charges of the latent image in accordance with the dose of radiation irradiated thereon at the interface between the recording photoconductive layer and charge transport layer. Thereafter, the radiation image stored in the detector is read out as electrical signals by scanning the reading light extending linearly in the direction substantially orthogonal to the longitudinal direction of the linear electrodes from the side of the second electrode layer in the longitudinal direction of the linear electrodes and detecting the charges stored in the detector, that is, when the reading light is irradiated on the detector, charge-pairs are generated in the reading photoconductive layer and either negative or positive charges of the charge-pairs couple with the charges of the latent image stored in the storage section of the detector, while the charges of opposite polarity are detected by charge amplifiers connected to the first or second linear electrodes, thereby the radiation image stored in the detector is read out as electrical signals.
Here, when reading out electrical signals from the radiation image detector by scanning the linear reading light as described above, the switches on the charge amplifiers are switched sequentially in the direction substantially orthogonal to the longitudinal direction of the linear electrodes at a predetermined timing for each scanning line of the reading light so that respective electrical signals, each corresponding to each of the pixels forming the radiation image are outputted sequentially from the charge amplifiers in accordance with the switching. Thus, the switching timing of the charge amplifiers for each scanning line must be synchronized according to the scanning of the reading light in the longitudinal direction of the linear electrodes. In this connection, devices for converting a mechanical traveling speed into an electrical pulse signal, such as linear or rotary encoders, have been separately provided, and the synchronization signals generated by these devices have been used to implement the switching for each scanning line.
When the synchronization signal is generated by the linear or rotary encoder described above, however, discrepancies may arise between the traveling speed of the reading light source and the synchronization signal outputted from the encoder, causing certain irregularities and the like to be developed in the radiation image formed by the electrical signals read out from the radiation image detector, thereby the image quality is degraded. Further, the encoder and the like must be provided separately, so that the reading device becomes more complicated, thereby downsizing of the reading device is difficult. Still further, it requires regular maintenance for mechanical adjustments.